1. Field of the Invention
The present invention relates to a display device as means for displaying information to a driver in a vehicle, and particular to a head-up display device.
2. Description of the Related Art
In a vehicle such as a automobile, a driver is given instrument information of various kinds of displays such as speed, the number of revolutions of an engine, etc., via a speedometer, a revolution-counter, etc., for example, in a so-called meter cluster (instrument panel) installed on a dashboard. Presently there can be used a head-up display device to display such information on a windshield over the dashboard (for example, Japanese Patent Application Laid-Open Publication No. 09-15555).
A driver sees a virtual image of a displayed image reflected a windshield in a head-up display device described in the Publication No. 09-15555. Therefore the driver perceives the displayed image in a space of the opposite side of the driver with respect to the windshield, i.e., the outside of a vehicle.
A position of a displayed image to be seen depends on a distance between an object of view and a windshield and a radius of curvature of a mirror surface positioned therebetween, in general. Anyway the driver sees a displayed image in the outside of the vehicle (the outside the windshield), by no means, the driver cannot perceives the displayed image in the inside of a vehicle (the inside of the windshield).
As described above, it is impossible to give the driver any images displayed in a both the spaces of the outside (the outside of a vehicle) and the inside (the inside of a vehicle) of the windshield even using a conventional head-up display device utilizing a virtual image.